What are the advantages of Variable frequency AC drives over DC drives?

there are many advantages as follow :

1- AC variable frequency is more reliable compare to DC 

2- in AC variable frequency can be controled by using booth frequency duty cycles and voltage values while DC driver can only control the voltage

3-due to the fact of frequency control, the AC variable frequency is is more suffecent in energy consumtion compare to DC drivers 

We can control the speed of motor through this formula in VFD Ns=120f/p if we change the frequency the speed will also change, no need to use the3 point  or4 point  DC starters

Variable frequency AC drives use conventional induction motors .

Induction motors are more rugged and require virtually zero maintenance.

Induction motors are smaller, lighter and less expensive than DC motors.

When the load attached to motor varies greatly AC Induction motors perform extremely good whereas the DC motor commutators / brushes might wear significantly.